Memory devices are typically provided as internal, semiconductor, integrated circuits in computers or other electronic devices. There are many different types of memory including random-access memory (RAM), read only memory (ROM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), and flash memory.
Flash memory devices have developed into a popular source of non-volatile memory for a wide range of electronic applications. Flash memory devices typically use a one-transistor memory cell that allows for high memory densities, high reliability, and low power consumption. Changes in threshold voltage of the cells, through programming of charge storage or trapping layers or other physical phenomena, determine the data value of each cell. Common uses for flash memory and other non-volatile memory include personal computers, personal digital assistants (PDAs), digital cameras, digital media players, digital recorders, games, appliances, vehicles, wireless devices, cellular telephones, and removable memory modules, and the uses for non-volatile memory continue to expand.
Flash memory and other non-volatile memories are often grouped into sections called “erase blocks.” Each of the cells within an erase block can be electrically programmed selectively by altering the threshold voltage of an individual cell from an initial state. However, cells of the erase block are erased, or reverted to their initial state, generally in a single operation across the entire block. Any data in the erase block that is to be retained by the memory device must first be copied to another location or buffer before performing the erase operation.
In part because of their large block sizes, NAND devices are primarily used for storing data, such as audio, video or image files. Such files are frequently read, but generally infrequently modified. Increasingly, however, NAND devices are being designed into embedded systems. Such systems have need for code and temporary parameter storage as well as data storage. However, code and parameter data requires relatively frequent modification, requiring frequent and extensive movement or buffering of the data in a block that is to be retained. As memory densities continue to increase, block sizes are also tending to increase, thus exacerbating this problem.
NAND flash is said to be able to work reliably until the number of program and erase (PE) cycles applied exceeds a value specified by the flash vendor. As a result, SSD vendors have designed drives to limit the number of PE cycles to stay below the specified limit on each device in the drive. This process of applying the same number of PE cycles to each block is known as wear leveling.
Traditional wear leveling works under the premise that no device should be used any more than the weakest device in the system. As a result, many blocks that have capability beyond the weakest of the population are left under utilized by traditional wear leveling.
Thus, a need still remains for a non-volatile memory management system. In view of the expanding applications of non-volatile memory into dynamic data management systems, it is increasingly critical that answers be found to these problems. In view of the ever-increasing commercial competitive pressures, along with growing consumer expectations and the diminishing opportunities for meaningful product differentiation in the marketplace, it is critical that answers be found for these problems. Additionally, the need to reduce costs, improve efficiencies and performance, and meet competitive pressures adds an even greater urgency to the critical necessity for finding answers to these problems.
Solutions to these problems have been long sought but prior developments have not taught or suggested any solutions and, thus, solutions to these problems have long eluded those skilled in the art.